综合地球物理方法在华南桂中海相残留盆地沉积相预测中的应用

Application of integrative geophysical methods to predicting sedimentary facies of marine residual basins in middle Guangxi province, China

沉积相研究是盆地隐蔽油气藏勘探中重要的研究内容之一,综合利用地球物理方法有效识别构造、岩性或沉积相差异是盆地隐蔽油气藏勘探的前提.本文基于重力、航磁、地震等综合地球物理资料,通过重磁异常正演剥离和剖面正反演拟合技术研究了华南桂中地区海相地层的密度分布特征,预测了岩相、沉积相的变化规律.研究发现,本区中、下泥盆统海相地层存在横向的岩性、岩相变化,研究区西北、东南部的台地相区重力异常高、岩石拟合密度值高;中部"X"型台地边缘相区重力异常杂乱、岩石拟合密度变化范围大;东部台沟相区重力异常低、岩石拟合密度值低.利用综合地球物理方法预测沉积相为盆地岩性圈闭汕气藏和生物礁油气藏勘探提供了新的研究思路,研究成果已得到初步检验,但还有待进一步完善与实践.

The sedimentary facies study is one of the key procedures in exploration of subtle reservoirs in basins, of which a prerequisite is effective identification of its structural, lithologic or lithofacies differences through integrated usage of geophysical methods. Based on geophysical data, including gravity, aeromagnetic and seismic data, this paper describes the density distribution characteristics of marine strata in middle Guangxi province, south China, and predicts the regularities of lithofacies and sedimentary facies changes in terms of potential field forward stripping and profile forward/inverse fitting. It is revealed that transversal lithologic and lithofacies changes exist in the marine strata of mid- and lower-Devonian series of the area. The platform zones in northwest and southeast of the area have high gravity anomalies and high fitting rock density. The ＂X＂-shaped platform-marginal facies zone in the middle is characterized by irregular gravity anomalies and a large variation range of fitted rock density. And the platform-trough facies zone in the east exhibits low gravity anomalies as well as low fitted rock density. Predicting sedimentary facies through integrative geophysical methods offers a new approach for exploration of lithologic trap reservoirs and bioherm reservoirs in basins. This method has been preliminarily proved, and needs further improvements and applications.